The present invention relates to an electric brake system, and particularly to an electronically controlled brake system based on electric brake mechanisms.
In recent years, there have been proposed and developed various electric brake systems, in which an electric brake actuator is controlled in response to a control signal from an electric-brake-system electronic control unit so as to vary the magnitude of braking force. The control signal value is based on the amount of depression of a brake pedal. One such electric brake system has been disclosed in Japanese Patent Provisional Publication No. 9-137841 (hereinafter is referred to as xe2x80x9cJP9-137841xe2x80x9d). The electric brake system disclosed in JP9-137841 is comprised of an electric brake actuator that advances and retracts a friction pad toward and away from a brake disk rotor, a thrust sensor that detects the magnitude of the pressure of the friction pad against the disk rotor, a position sensor that detects the position of the friction pad, and an electronic control unit that controls the operation of the electric brake actuator. The control unit has a thrust control function that controls the operation of the electric brake actuator responsively to a thrust indicative signal from the thrust sensor, and a position control function that controls the operation of the electric brake actuator responsively to a pad-position indicative signal from the position sensor. Concretely, a friction-pad position obtained at a timing that braking operation terminates and the magnitude of thrust or pressure of the friction pad against the disk rotor becomes zero is regarded as a braking initiation position. The friction pad is moved away from the braking initiation position by a predetermined distance or a predetermined clearance, each time braking operation terminates. Thus, it is possible to keep the pad-to-rotor clearance constant depending on the degree of friction-pad wear. However, in presence of undesired deflection or uneven wear of the disk rotor, and thermal expansion or thermal contraction, such a conventional electric brake system is still inadequate from the viewpoint of more-precise detection of the braking initiation position.
FIG. 10 shows an example of a friction-pad position versus thrust characteristic diagram. As can be seen from the characteristic diagram of FIG. 10, during the initial stage of braking operation, the friction pad is shifted toward the disk rotor from a state wherein the friction pad is held away from the disk rotor by a certain pad-to-rotor clearance, i.e., an initial pad-to-rotor clearance before a braking operation, and then brought into contact with the disk rotor (see an initial contact position Po in FIG. 10). For example, when downhill braking is continuously executed for a long time period from the initial stage of braking operation, the thrust of early stages of braking rises based on an initial-braking-period friction-pad rigidity characteristic (corresponding to a gradient of the right-hand side straight line shown in FIG. 10). However, when the downhill braking operation is released, owing to thermal expansion and reduced rigidity of the friction pad, arising from a great deal of frictional heat created during braking operation of the electric brake system, the thrust never falls in accordance with the initial-braking-period friction-pad rigidity characteristic. As can be appreciated from the characteristic diagram of FIG. 10, the thrust of last stages of the braking operation tends to fall based on a last-braking-period friction-pad rigidity characteristic (corresponding to a gradient of the left-hand side straight line shown in FIG. 10) different from the initial-braking-period friction-pad rigidity characteristic. That is, owing to thermal expansion and reduced rigidity of the friction pad, there is an increased tendency for the contact position of the friction pad with the disk rotor to become offset from initial contact position Po.
Suppose that the predetermined pad-to-rotor clearance is determined based on the contact position that is affected by thermal expansion and reduced rigidity of the friction pad and that is offset from initial contact position Po. In this case, if the friction pad is cooled during the non-braking state with the brake pedal undepressed and thus the friction pad is heat-contracted, the actual pad-to-rotor clearance varies from the previously-discussed initial pad-to-rotor clearance. Additionally, a heating state of the friction pad during braking operation always varies depending on the braking time, braking energy, non-braking time, vehicle speed during the non-braking period, and the like. The pad-to-rotor clearance tends to vary every braking operation. In particular, on four-wheeled vehicles, there is an increased tendency for the pad-to-rotor clearances at four road wheels to become different from each other. This means that there is a deviation of a timing of initiation of braking action (or braking force) at one of four road wheels from a timing of initiation of braking action (or braking force) at the other wheel, thereby resulting in a poorly balanced braking action between one of four road wheels and the other wheel and thus giving the driver a poor braking feel.
Accordingly, it is an object of the invention to provide an electric brake system, which avoids the aforementioned disadvantages.
It is another object of the invention to provide an electric brake system of an automotive vehicle with an electric-brake-system electronic control unit capable of electronically controlling the magnitude of pressure of a brake friction pad (a brake friction material) against a brake disk rotor (a rotary body being rotatable together with a road wheel), which is capable of maintaining a better braking balance among four road wheels of the vehicle by keeping the pad-to-rotor clearance at each of the road wheels constant, irrespective of the degree of friction-pad wear and the presence or absence of thermal expansion and reduced rigidity of the pad.
In order to accomplish the aforementioned and other objects of the present invention, an electric brake system comprises a brake manipulated variable sensor that detects a driver""s brake manipulated variable of a brake operating device, an electric wheel brake mechanism having a pair of brake friction pads that are opposite to each other for sandwiching therebetween a disk rotor rotatable together with a road wheel and for producing a braking force resulting from braking torque application to the disk rotor, a first brake friction pad thrust sensor that detects a first pressure of a first one of the brake friction pad pair against one side wall of the disk rotor, a second brake friction pad thrust sensor that detects a second pressure of the second brake friction pad against the other side wall of the disk rotor, a control unit configured to be electronically connected to the brake manipulated variable sensor, the first and second brake friction pad thrust sensors and the electric wheel brake mechanism, for controlling the electric wheel brake mechanism responsively to the brake manipulated variable, and the first and second pressures, and the control unit causing a movement of the brake friction pad pair into contact with the disk rotor when the brake operating device is conditioned in an inoperative state, and detecting a position of the brake friction pad pair, at which the first and second pressures become greater than respective predetermined threshold values during the movement of the brake friction pad pair into contact with the disk rotor, as a braking initiation position.
According to another aspect of the invention, an electric brake system comprises a brake manipulated variable sensor that detects a driver""s brake manipulated variable of a brake operating device, an electric wheel brake mechanism having a pair of brake friction pads that are opposite to each other for sandwiching therebetween a disk rotor rotatable together with a road wheel and for producing a braking force resulting from braking torque application to the disk rotor, a brake friction pad thrust sensor that detects a pressure of either one of the brake friction pad pair against the disk rotor, a control unit configured to be electronically connected to the brake manipulated variable sensor, the brake friction pad thrust sensor and the electric wheel brake mechanism, for controlling the electric wheel brake mechanism responsively to the brake manipulated variable, and the pressure of the one brake friction pad against the disk rotor, the control unit comprising a maximum disk-rotor thickness angular position detecting section that detects an angular position of the disk rotor at which a disk rotor portion has a maximum thickness, and the control unit causing a movement of the brake friction pad pair into contact with the disk rotor when the brake operating device is conditioned in an inoperative state, and detecting a position of the brake friction pad pair, at which the pressure becomes greater than a predetermined threshold value at the angular position of the disk rotor corresponding to the disk rotor portion having the maximum thickness during the movement of the brake friction pad pair into contact with the disk rotor, as a braking initiation position.
According to a further aspect of the invention, an electric brake system comprises a brake manipulated variable sensing means for detecting a driver""s brake manipulated variable of a brake operating device, an electric wheel brake means having a pair of brake friction pads that are opposite to each other for sandwiching therebetween a disk rotor rotatable together with a road wheel and for producing a braking force resulting from braking torque application to the disk rotor, a first brake friction pad thrust sensing means for detecting a first pressure of a first one of the brake friction pad pair against one side wall of the disk rotor, a second brake friction pad thrust sensing means for detecting a second pressure of the second brake friction pad against the other side wall of the disk rotor, a brake control means configured to be electronically connected to the brake manipulated variable sensing means, the first and second brake friction pad thrust sensing means and the electric wheel brake means, for controlling the electric wheel brake means responsively to the brake manipulated variable, and the first and second pressures, and the control means causing a movement of the brake friction pad pair into contact with the disk rotor when the brake operating device is conditioned in an inoperative state, and detecting a position of the brake friction pad pair, at which the first and second pressures become greater than respective predetermined threshold values during the movement of the brake friction pad pair into contact with the disk rotor, as a braking initiation position.
According to a still further aspect of the invention, an electric brake system comprises a brake manipulated variable sensing means for detecting a driver""s brake manipulated variable of a brake operating device, an electric wheel brake means having a pair of brake friction pads that are opposite to each other for sandwiching therebetween a disk rotor rotatable together with a road wheel and for producing a braking force resulting from braking torque application to the disk rotor, a brake friction pad thrust sensing means for detecting a pressure of either one of the brake friction pad pair against the disk rotor, a control means configured to be electronically connected to the brake manipulated variable sensing means, the brake friction pad thrust sensing means and the electric wheel brake means, for controlling the electric wheel brake means responsively to the brake manipulated variable, and the pressure of the one brake friction pad against the disk rotor, the control means comprising a maximum disk-rotor thickness angular position detecting section that detects an angular position of the disk rotor at which a disk rotor portion has a maximum thickness, and the control means causing movement of the brake friction pad pair into contact with the disk rotor when the brake operating device is conditioned in an inoperative state, and detecting a position of the brake friction pad pair, at which the pressure becomes greater than a predetermined threshold value at the angular position of the disk rotor corresponding to the disk rotor portion having the maximum thickness during the movement of the brake friction pad pair into contact with the disk rotor, as a braking initiation position.
According to another aspect of the invention, a method of detecting a braking initiation position of an electric brake system with a brake manipulated variable sensor detecting a driver""s brake manipulated variable, an electric wheel brake mechanism having a pair of brake friction pads that are opposite to each other for sandwiching therebetween a disk rotor rotatable together with a road wheel and for producing a braking force resulting from braking torque application to the disk rotor and based on the brake manipulated variable, a first brake friction pad thrust sensor detecting a first pressure of a first one of the brake friction pad pair against one side wall of the disk rotor, and a second brake friction pad thrust sensor detecting a second pressure of the second brake friction pad against the other side wall of the disk rotor, the method comprises causing a primary movement of the brake friction pad pair into contact with the disk rotor when a predetermined time period has expired from a time when a brake pedal has been recovered to an inoperative state, and detecting a position of the brake friction pad pair, at which the first and second pressures become greater than respective predetermined threshold values during the primary movement of the brake friction pad pair into contact with the disk rotor, as the braking initiation position.
According to another aspect of the invention, a method of detecting a braking initiation position of an electric brake system with a brake manipulated variable sensor detecting a driver""s brake manipulated variable, an electric wheel brake mechanism having a pair of brake friction pads that are opposite to each other for sandwiching therebetween a disk rotor rotatable together with a road wheel and for producing a braking force resulting from braking torque application to the disk rotor and based on the brake manipulated variable, and a brake friction pad thrust sensor detecting a pressure of either one of the brake friction pad pair against the disk rotor, the method comprises detecting an angular position of the disk rotor at which a disk rotor portion has a maximum thickness, causing a primary movement of the brake friction pad pair into contact with the disk rotor when a predetermined time period has expired from a time when a brake pedal has been recovered to an inoperative state, and detecting a position of the brake friction pad pair, at which the pressure becomes greater than a predetermined threshold value at the angular position of the disk rotor corresponding to the disk rotor portion having the maximum thickness during the primary movement of the brake friction pad pair into contact with the disk rotor, as the braking initiation position.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.